System for binaural transmission of signals



H. AFFEL SYSTEM FORBIl\1f1U"i,/-J;.l TRANSMISSION. OF SIGNALS April 17, 1928. I v1,666,158

Filed Der. 5 1. 1.925

INVENTOR ggg/w WL ATTORNEY Patented pr. 17, 1928.

NETE@ STATES insana g satana asi-uca.'

HERMAN A. AFFEL, OF MAPLEWOOD, NEW JERSEY, fASSIGINOR TO AMERICAN TELE- PHONE `.AND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK.

SYSTEM Fon BINAURAL TRANSMISSION on sIGNALs.

Application 'led December 31, 1925. Serial No.. 78,710.`

This invention relates to high frequency signaling systems, and'particularly to a system of the binaural type by means ofwhich it is possible to give to a listener an idea of ,the position of the source of sound producmust therefore be capable of conveymg these ing the transmitted signal.

In a system for the dissemination' of speech, music or other sounds such as a radio broadcast or a wire distributing system, it is desirable to create within the listener a sense of the position from which the sound emanates; for example, it is particularly satisfying to be able to follow the movement of participants during the broadcasting ofa play or to know the source of individualelements entering into the orchestration of a musical selection.

This invention resides in a high frequency transmission system which may be either' of the radio broadcast or the wire distributing type which is adapted to give to the listener at the receiving station a sense of the rela-` tive positionof the sound that is conveyed electrically over the transmission system. e

The conveyance of such sense of position requires the transmission of two signals practically` identical when separately con sidered but containing a small phase and amplitude difference such as is necessary to produce the same position discrimination as is afforded ,by the direct transmission of sound to the ears. The electrical circuit relations with a perfect balance of phase and amplitude, because if one channel' of transmission is distorted in somewhat different manner from the other, the result is somewhat negatived.

This invention will be clearly understood from the following description when read in connection with the attached drawing, ofv

which Figure 1- shows schematically an arrangement embodying the invention, and Fig. 2 shows graphically the relations between the carrier and side band currents of the system. In Fig. 1 the microphones P1 and P2 rep:p resent symbolically any means for picking up sounds to be transmitted electrically over a high frequency transmission system to a listenerl ata distant receiving station. These microphones are separatedV preferably by a distance equal to the separation between the ears of the average person, and

a screen suchy as is indicated by the line l may be inserted between the microphones in orderito simulate the barrier between the ears of a human being.' The microphone P1 is connected by means of the circuit 2 with the modulator M1, the connection being effected by the transformer 3. This modulator is of the well known carrier `suppression type, comprising the tubes 4 and 5 sym.- metrically arranged with respect to the input and the output circuits and having a,

T1 is connected. Band filters may be insorted in circuit 9 between the-transformers 8 and 12 and the point of connection of the antenna, or they may be insertedraln the antenna. And anamplifier or amplifiers may be connected either with the circuit 9 or the antenna T1 to raise the level of transmission.

lThe microphone P2 is connected by the circuit 10 with the modulator M2-Which is preferably similar to M1. The circuit 10 is coupled'b the transformer 11 with the input side o the modulator M2, which modulator has its output side connected by the transformer 12 with the output circuit 9 to which the antenna T1 is connected. The oscillator 6 is connected with the common conductor of the modulator 'M2 by means of the transformer 13. .-Inserted between theoscillator 6 and the transformer 13 isa phaseshifter PS1, thefunction of .which is to control the phase of the carrier oscillations applied by I' the source 6 to the input circuit of the modulator M2. The receiving station comprises an antenna R1 which is bridged across the common receiving circuit 14. This circuitis connected with .the detector D1 by the transformer 15 and with the detector D2 by vthe transformer 16. A carrier frequency oscillator 17 is connected with the input-sides of both detectors. The connection betweenthe oscillator land the detector D2 includes a phase shifter PS2', the function of which is -to control `the phase angle of the carrier oscillations applied to the latter detector. The. output circuit of detector D1 islconnected by the transformer 18 with the receiver 19 and similarly the output circuit of detector Da is connected by transformer 2O with the receiver 21.

It is recognized that two carriers 90 de-y phones P1 and P2, but since the source is not equidistant from both microphones, the ef feet upon them will occur at different.. instants of time. The current set up inthe circuit 2 by the action of the sound upon the microphone .P2 will impress a voltage across the secondary winding of the transformer 3, which will modulate the carrier designated C impressedV by the source 6 upon the secondary winding of the transformer 7 which is connected with the common conductor of the modulator M1. This will produce two side bands S1 and S2, which, as shown in Fig. 2, will have at any instant of time the same phase angle with respect .to the carrier C. Since the `carrier is suppressed by the modulator Ml the side bands will be transmitted through the transformer 8 to the circuit 9 and will be radiated by the antenna T1. The effect of the sound upon the microphone P2producesa current in the circuit 10 which induces a potential across the seco'ndary winding of transformer 1-1, and this in turn serves to modulate oscillations of the carrier frequency impressed upon the secondary windingof the transformer 13 which is connected with the conductor of the modulator M2.' vThe carrier oscillations pass through the phase shifter PS1 which is adjusted to render the carrier oscillations applied to modulator M2 90 degrees out of phase with the carrier oscillations applied to modulator M2. A s shownfin Fig. 2, the carrier vector C is 90 degrees out of phase with the vector C. Since the modulator M2 isI of' the carrier suppression type, only the side bands'Sl and S2 will be transmitted by the transformer 12 to the output circuit 9 and thence to the antenna T1.

These four side bands will be received by the antenna R1 and impressed upon the input circuit 14 and will in turn be impressed by the transformers 15 and 16 upon both of the detectors D1 and D2. Carrier oscillations from the source 17 will also be impressed upon the detectors. `These carrier oscillations have the same frequency as those produced by the source 6 at the transmitting station. The oscillations applied to the detector D2 will be shifted in phase by 90 degrees from the oscillations applied to the detector D1.' The phase relationships ofthe This is clearly shown in Fig. 2 :in

carriers and the side bands must be as shown in F ig. 2. That is to say, the `frequency of the receiving carrier must be exactly the same as that of the sending carrier, and the phase must be adjusted so that the relationship of Fig. 2 obtains. ThusA it will be seen that although the four side bands S1, S2, S1', S2 are presentin the yinput'eircuits of both detectors, only the side bands S1 and S2 will be detected by D1 and only the side bands S1 and S2 will be detected by D2. The audible signal produced by Dl will be impressed by the transformer 18 upon the ref ceiver 19, and similarly the double signal produced by D2 will be impressed by the transformer 20 upon the receiver 21. The effect of the sound produced by lthese receivers upon thelistener conveys to him an idea of `the position of the source of sound vthat created the variationsl in -the separate channels from which they were transmitted to the listener, from a distant point. 2

The principle upon which this invention rests is' that two carriers, 90 degrees .'di s placed in time phase, may be modulated to produce independent side band systems. Tfn one set of sidev bands is detected by a carrier in phase with the symmetrical mean of result, whereas if the carrier'is 90 degrees` out of phase with the symmetricalI mean of the side bands, the signal will `not-bedetected. While such a system is'praetically difficult to employ in the transmissionV of iin-1 related signals, it is' entirely feasiblef'for the conveyance of a single signal for the`production of binaural effect. The cross-talkbetween channels in the latter case will not produce quality deterioration butwills'imply reduce the effectiveness of the binaural result. v

While this invention has been disclosed-"as embodied in a particular form, it is capable of embodiment in other and different forms without departing from the spirit and scopev of'theappended claims.

'What is claimed is:

1. In a system for the binaural transmission of signals, the combination with a transmitting circuit of two similar input circuits phone and a modulator, a source of carrier current common to both modulators, and a phase shifter interposed between the said source and' one of the said modulators.

connected therewith, each having a micro' 2. In a system for the binaural transmis# the said one of the modulators 90 out of phase with the oscillations applied to the other modulator.

3. In a system for the binaural transmission of signals, the combination with two branch circuits each having a microphone and a modulator, both microphonesbeing in the same plane but separated in space, a source of carrier oscillations connected with both modulators, and a phase shifter interposed between the said source and one of said modulators to render the oscillations 90 out of phase with those applied to the other -Iof `the said modulators. p l n 4. In a system for the binaural transmission of signals, the combination with a transmitting station comprising two similar branch circuits connected with a transmitl ting medium, each branch circuit having a posed between one `detector and the said source of oscillations. Y

5. In a system for the binaural transmission of signals, the method which consists in one circuit differing in phase by 90 from.

those in the other circuit, suppressing the carrier oscillations, and transmitting the bands resulting from both'modulating processes.

6. In a system for sion of si als, the method which consists in transmitting two sets of side bands resulting from modulating by the same signal carrier oscillations of the same frequency but diering in phase by'90, receiving 'the said sets of side bands, separately beating the received side bands with carrier oscillations' In testimony whereof Iv have signed myv name to this specification` this 30th day of December, 1925.

the binaural transmisu HERMAN'A. AFFEn. y 

